Britain's top athletes last night received a further warning "to be extremely careful" following the furore surrounding Black Country athlete Mark Lewis-Francis.

Birchfield Harrier Lewis-Francis was stripped of the European Indoor 60 metres silver medal he won in Madrid in March, and received a public warning from UK Athletics after traces of cannabis were found in a post-race drugs sample. The Olympic 4x100m gold medallist insisted he has never smoked cannabis, claiming the positive test was because he may have been in the presence of people who were smoking it and that he passively inhaled their smoke.

UKA performance director Dave Collins believes what has happened should serve as yet another wake-up call to all athletes to be increasingly vigilant in their social lives. When asked whether he was surprised Lewis-Francis chose to condone people blowing cannabis smoke in his direction, Collins said: "I am not surprised, but disappointed he didn't make that call.

"I'm sure it's a call he will make in the future. Mark has learned substantially from this, and if our other athletes learn cannabis is on the banned list and they need to be extremely careful in their lifestyles, then that's fine.

Collins, though, refused to be drawn on whether he believed Lewis-Francis' claims that he only passively inhaled, rather than smoked cannabis directly.

"How it got into the body, be it by passive smoking or actual inhalation, is completely coincidental to the penalty and to the positive drug test."The athlete is liable for what is in his or her body."